Terrorists have staged their biggest advance in years over the past week, capturing large parts of the northern city of Aleppo, the country’s largest, as well as towns and villages in southern parts of the northwestern Idlib province.

The offensive is being led by led by Hayat Tahrir al-Sham (HTS), as well as Turkiye-backed fighters known as the Syrian National Army (SNA). Both groups have in recent years entrenched themselves in northwest Idlib province and parts of northern Aleppo, with HTS considered the dominant force.

A video circulating on social media showed HTS leader Abu Mohammed al-Golani on Wednesday surrounded by supporters as he walked in front of the Citadel of Aleppo, a large medieval fortified palace in the centre of the old city.

The war between President Bashar Assad and his allies – including Russia and Iran – and the array of militant groups seeking his overthrow has killed an estimated half-million people during the past 13 years.

Syrian state media SANA on Wednesday said militants retreated some 20km (12 miles) from government-held Hama, Syria’s fourth-largest city, as government troops backed by Russian airpower entrenched themselves in the outskirts.

Fierce fighting has raged for days as Damascus fears that militants will make their way into the city as they did over the weekend into Aleppo.

If militants seize Hama city and control the province, it could leave the coastal cities of Tartous and Lattakia isolated from the rest of the country. Lattakia is a key political stronghold for Assad and Syria’s Alawite community, as well as a strategic Russian naval base.

Tens of thousands have been displaced by the fighting, which started last week, Geir Pedersen, the UN special envoy for Syria, stated Tuesday.

“If we do not see de-escalation and a rapid move to a serious political process, involving the Syrian parties and the key international players, then I fear we will see a deepening of the crisis,” Pedersen said in an address the UN Security Council.

“Syria will be in grave danger of further division, deterioration, and destruction,” he added.

Turkiye, which backs Syria’s opposition, has called on Assad to reconcile with opposition forces and include them in any political solution to end the conflict.

Ankara has been seeking to normalise ties with Syria to address perceived security threats from groups affiliated with Kurdish fighters along its southern border and to help ensure the safe return of more than 3 million Syrian refugees.

Assad has insisted that Turkiye’s withdrawal of its military forces from northern Syria be a condition for any normalisation between the two countries.

Damascus refers to the opposition as “terrorists”, and Assad has promised to respond to the offensive with an iron fist.